This lesson helps introduce students to the concept that temperature causes molecules and atoms to move faster and farther apart, which in turn causes the change from solid to liquid, and liquid to gas.

Fairy Circles

Mysterious “fairy circles” on African plains are caused by termites, which destroy patches of grass but help the surrounding grass thrive.

Transcript

Fairy circles’ cause and effect. I’m Bob Hirshon and this is Science Update.

On the edge of the Namibian desert, mysterious so-called “fairy circles” appear. They’re circles of bare dirt, surrounded by a ring of thick perennial grass.

Now, University of Hamburg biologist Norbert Juergens has found that the circles are made by sand termites, which eat underground grass roots. Although that leaves the inner circle barren, it also helps the soil hold water—because there are no plants to take up the water and release it into the air. Through the long dry season, the water sustains both the termites and the grasses on the circle’s perimeter.

Juergens:The termites create a permanent water store, and a permanent plantation of grasses.

These perennial grasses also attract other insects and small mammals. So the termites’ fairy circles actually create a rich ecosystem, in what might otherwise be a barren landscape. I’m Bob Hirshon for AAAS, the Science Society.

Making Sense of the Research

“Fairy circles,” first observed in 1971, occur in a long, narrow band at the edge of the desert, far from any human village, in the southern African country of Namibia. For decades, scientists have debated what causes them. This study not only pinpoints the culprit but also reveals that fairy circles are a part of a complex ecosystem.

Termites have long been a suspect in the fairy circle mystery, but Juergens' team is the first to show conclusive evidence that the insects really do create them. They did this by closely examining hundreds of fairy circles up and down 1,200 miles of desert, and found that sand termites were the only organism present in every single location. What's more, close observation revealed that the termites eat plant roots inside the circle, preventing anything from growing there.

But what kills plants on the inside of the circle actually promotes plant growth around the edges. The climate in fairy circle territory is too dry to sustain plants year-round. One would expect only short-lived plants to pop up during the brief rainy season. If they did, much of the water in the soil would escape into the atmosphere through transpiration: the release of water vapor through pore-like openings in a plant's leaves, stems, and flowers.

The sand termites not only destroy plants within a fairy circle, but also dig tunnels and burrows, which make the soil airy and porous. That allows rainwater to seep down to cooler depths, where it's protected from evaporating in the sun. So the termites' work, in the form of eating plant roots and digging tunnels, allows water to be stored in the soil throughout the year.

That water, in turn, nourishes grasses that grow around the edges of the fairy circle—grasses that couldn't survive year-round without the stored water. And those grasses, in turn, attract other insects and small mammals that wouldn't otherwise have a reason to forage in such a desolate place. So by destroying one type of plant life, the termites actually make it possible for many other kinds of life to thrive. The research shows that just one species can have a big impact on any ecosystem.

Now try and answer these questions:

What are fairy circles? Where do they occur?

How did the researchers establish that termites create fairy circles?

In what two ways do the termites make it possible for the soil to hold water? How does that impact the ecosystem?

What do you think would happen if the termites died out? How might this affect other areas besides those in which the fairy circles occur?

You may want to check out the April 5, 2013, Science Update Podcast to hear further information about this Science Update and the other programs for that week. This podcast's topics include: Scientists attempt to bring back an extinct frog, mummies showing signs of heart disease make researchers rethink assumptions about lifestyle and diet, the mysterious death zone within African “fairy circles” explained, and a miniature laboratory under the skin monitors blood chemistry.

Humans, too, affect water retention in soils, often with unexpected consequences. Find out about some examples in the Science Updates Tree Torture and Florida Freezes.

In the first installment of the 2011 BioBlitz BobCast, Science Update reporter Bob Hirshon launches a series of live video features on biodiversity.